The Collaborative International Dictionary of English v.0.48:

obligated \obligated\ adj.
   1. under a moral obligation to someone.

   Syn: beholden(predicate).
        [WordNet 1.5]

   2. under a legal obligation to someone.

   Syn: indebted.
        [WordNet 1.5]

   3. owing gratitude or recognition to another for help or
      favors etc. Opposite of unobligated. [Narrower terms:
      supposed(predicate), required ]

   Syn: indebted.
        [WordNet 1.5]

The Collaborative International Dictionary of English v.0.48:

Obligate \Ob"li*gate\, v. t. [imp. & p. p. {Obligated; p. pr. &
   vb. n. Obligating.] [L. obligatus, p. p. of obligare. See
   Oblige.]
   1. To bring or place under obligation, moral or legal; to
      hold by a constraining motive. "Obligated by a sense of
      duty." --Proudfit.
      [1913 Webster]

            That's your true plan -- to obligate
            The present ministers of state.       --Churchill.
      [1913 Webster]

   2. To bind or firmly hold to an act; to compel; to constrain;
      to bind to any act of duty or courtesy by a formal pledge.
      [1913 Webster]

            That they may not incline or be obligated to any
            vile or lowly occupations.            --Landor.
      [1913 Webster]

WordNet (r) 3.0 (2006):

obligated
    adj 1: caused by law or conscience to follow a certain course;
           "felt obligated to repay the kindness"; "was obligated to
           pay off the student loan" [ant: unobligated]

Moby Thesaurus II by Grady Ward, 1.0:

33 Moby Thesaurus words for "obligated":
   affianced, answerable for, assured, beholden, beholden to,
   betrothed, bound, bounden, bounden to, chargeable, committed,
   compromised, contracted, duty-bound, engaged, guaranteed,
   in duty bound, indebted to, intended, liable, obligate, obliged,
   obliged to, pledged, plighted, promised, responsible, saddled,
   sworn, tied, under obligation, underwritten, warranted